A footplate disclosed in DE 200 17 862 U1 has one channel for engaging the rail of one type of guide. The channel has two restrictions, one located at each longitudinal end of the footplate. The width of each restriction is defined, on the one hand, by a fixed side wall in the channel and, on the other hand, by an adjustable side wall. The adjustable side wall may be adjusted transversely to the longitudinal direction by an adjustment mechanism thereby altering the width of the channel. The adjustment mechanisms are for fine-tuning clearance between the channel and the rail so that the footplate is guided along the guide without wobbling, as it were, in an exactly linear manner. These restrictions are referred to as “single-restrictions” because they can alter the width of only one channel.
A footplate disclosed in DE 36 06 525 has two channels on its lower side. Each channel can engage the rail of a different type of guide. The two channels are parallel to each other and are, in effect, two parts of a “dual-restriction”, albeit a non-adjustable dual-restriction because it cannot alter the width of either channel.
The present invention relates to a footplate that has two channels. Each channel can engage the rail of a different guide. The object of the invention is to ensure exact linear guidance of the footplate no matter which guide is used.
The present invention is a footplate for a power tool for guiding the tool along a guide, the footplate comprising on its lower surface at least one dual-restriction, wherein the first part of each dual-restriction is for engaging a rail extending in a longitudinal direction of a first guide on the upper surface of said first guide and the second part of each dual-restriction is for engaging a rail extending in a longitudinal direction of a second different guide on the upper surface of said second guide, wherein the first and second parts of each dual-restriction each has a fixed side wall, and wherein the first and second parts of each dual-restriction have an adjustable side wall arranged opposite to a respective fixed side wall. The adjustable side walls may be parts of separate components or different sides of one component. The adjustable side walls can adjust the clearance at the dual-restriction to ensure linear guidance of the footplate along the guide.
Preferably, the width between the fixed and adjustable side walls, when measured in a direction transverse to the longitudinal direction, is adjustable by an adjustment mechanism. One adjustment mechanism per dual-restriction makes efficient use of the materials for making the footplate which reduces the cost and complexity of manufacturing.
Preferably, the adjustable side walls are both located between the fixed side walls. As such, the adjustable side walls are adjacent each other and in the middle of the dual-restriction. This close proximity makes the adjustable side walls easily accessible to the adjustment mechanism.
Preferably, the adjustment mechanism comprises a rotatable eccentric element located between the adjustable side walls. As such, the eccentric element can adjust the width between fixed and adjustable side walls simply by rotating about its own axis. Naturally, the width between fixed and adjustable side walls of the first part of the dual-restriction can only increase while the width between fixed and adjustable side walls of the second part of the dual-restriction decreases, and vice versa. This is not important because the footplate is normally only used with one guide with one type of rail at any one time.
Preferably, the adjustable side walls are opposing sides of a perimeter wall surrounding the eccentric element. This dispenses with the need for additional components between the eccentric element and the rail of the guide upon which the footplate is positioned. In other words, the perimeter wall of the eccentric element slides directly against the rail.
Preferably, the perimeter wall is a cylindrical wall arranged eccentrically in relation to the axis of rotation of the eccentric element. This ensures that the eccentric element can adjust and fine-tune the width between fixed and adjustable side walls gradually and precisely.
Preferably, the eccentric element is secured to the footplate by a fixing bolt connected to a bearing portion of the footplate, wherein the fixing bolt can be unfastened or fastened to enable or disable rotation of the eccentric element, respectively. The fixing bolt performs the function of rotational axis and fastening means for the eccentric element. This is a simple and inexpensive means of enabling or disabling rotation of the eccentric element.
Preferably, the adjustment mechanism comprises a manually accessible actuating member for rotating the eccentric element. As such, the eccentric element can be easily manipulated by the user of the tool. The actuating member may take the form of a knurled, cylindrical knob.
Preferably, the eccentric element can be rotated 360°. This facilitates easy use by left-handed and right-handed users of the tool.
Alternatively, the adjustment mechanism comprises two arms, each arm arranged at one end to pivot about a common pivot point so that an open mouth may be formed at the other ends of the arms, and a wedge arranged to move within the mouth according to the position of a control device, whereby movement of the wedge into the mouth forces the arms to pivot apart to reduce the width between the fixed and adjustable side walls, and whereby movement of the wedge away from the mouth allows the arms to pivot closer to each other to increase the width between the fixed and adjustable side walls. As a result of its wedge action this design of adjustment mechanism has the advantage of being highly resistant to any external forces changing the position of the adjustable side walls.
Preferably, each arm of the alternative design of adjustment mechanism has a shoulder and one shoulder protrudes away from the other shoulder in the transverse direction, whereby one shoulder is the adjustable side wall of the first part of the dual-restriction and the other shoulder is the adjustable side wall of the second part of the dual-restriction.
Preferably, the control device of the alternative design of adjustment mechanism is a grub-screw threadedly engaged with an externally accessible hole in the footplate, whereby rotation of the grub-screw into the footplate moves the wedge into the mouth and whereby rotation of the grub-screw out of the footplate allows the wedge to move out of the mouth. More preferably, each arm is biased to pivot towards the other arm.